=pod

=head1 NAME

EVP_PKEY_CTX_new, EVP_PKEY_CTX_new_id, EVP_PKEY_CTX_dup, EVP_PKEY_CTX_free -
public key algorithm context functions.

=head1 SYNOPSIS

 #include <openssl/evp.h>

 EVP_PKEY_CTX *EVP_PKEY_CTX_new(EVP_PKEY *pkey, ENGINE *e);
 EVP_PKEY_CTX *EVP_PKEY_CTX_new_id(int id, ENGINE *e);
 EVP_PKEY_CTX *EVP_PKEY_CTX_dup(EVP_PKEY_CTX *ctx);
 void EVP_PKEY_CTX_free(EVP_PKEY_CTX *ctx);

=head1 DESCRIPTION

The EVP_PKEY_CTX_new() function allocates public key algorithm context using
the algorithm specified in B<pkey> and ENGINE B<e>.

The EVP_PKEY_CTX_new_id() function allocates public key algorithm context
using the algorithm specified by B<id> and ENGINE B<e>. It is normally used
when no B<EVP_PKEY> structure is associated with the operations, for example
during parameter generation of key genration for some algorithms.

EVP_PKEY_CTX_dup() duplicates the context B<ctx>.

EVP_PKEY_CTX_free() frees up the context B<ctx>.

=head1 NOTES

The B<EVP_PKEY_CTX> structure is an opaque public key algorithm context used
by the OpenSSL high level public key API. Contexts B<MUST NOT> be shared between
threads: that is it is not permissible to use the same context simultaneously
in two threads.

=head1 RETURN VALUES

EVP_PKEY_CTX_new(), EVP_PKEY_CTX_new_id(), EVP_PKEY_CTX_dup() returns either
the newly allocated B<EVP_PKEY_CTX> structure of B<NULL> if an error occurred.

EVP_PKEY_CTX_free() does not return a value.

=head1 SEE ALSO

L<EVP_PKEY_new(3)|EVP_PKEY_new(3)>

=head1 HISTORY

These functions were first added to OpenSSL 1.0.0.

=cut
